There's a logical fallacy in there: Just because machines don't buy widgets, doesn't mean people disappear. They just get other jobs and continue to buy widgets. Buying widgets is not dependent on people making them.
Of course, there have to be other jobs available! If there are none because machines make everything, then you might have a problem. Most of the hard-core unemployment problems are because people like coal miners don't want to move somewhere else where their are jobs not mining coal. No conceivable government action is going to bring back those coal mining jobs, nor should it.